Incidental Paratracheal Air Cyst in Papillary Thyroid Cancer Patient: a Case Report

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Case Report

Incidental paratracheal air cyst in papillary thyroid cancer patient: a case report

Min Jhi Kim^, Hera Jung, Cheong Soo Park

Department of Surgery, CHA Ilsan Medical Center, Cha University School of Medicine, Goyang-si, Gyeonggi-do, South Korea Correspondence to: Cheong Soo Park, MD, PhD. Department of Surgery, CHA Ilsan Medical Center, Cha University School of Medicine, 1205, Jungang-ro, Ilsandong-gu, Goyang-si, Gyeonggi-do, South Korea. Email: [email protected].

Abstract: Paratracheal air cyst (PTAC) is a collection of air in the right posterior side of the trachea with an uncertain etiology. We report a papillary thyroid cancer patient with a PTAC that was removed during thyroid cancer surgery. A 68-year-old woman was diagnosed with right papillary thyroid cancer with suspicion of central lymph node metastasis. She had a history of hypertension and a rear-end collision car accident 20 years prior. On computed tomography, an ovoid cyst was incidentally found in the paratracheal region at the thoracic inlet level. Emphysematous lung with an obstructive lung defect was noted without any symptoms. Bilateral total thyroidectomy with ipsilateral central compartment neck dissection was indicated for the patient. During surgery, removal of the cyst was inevitable for complete central neck dissection. Histopathologic analysis revealed an etiology of tracheal mucus sprouting through weak trachea points. No postoperative complications occurred. The patient continued on levothyroxine medication without further radioactive iodine therapy. After 6 months, follow-up ultrasound showed no evidence of recurrence. We hypothesized that obstructive lung disease with impaired lung function or trauma history might have contributed to the development of PTAC. Future studies are needed to determine if PTACs have any association with obstructive lung disease or trauma.

Keywords: Paratracheal air cyst (PTAC); trachea; computed tomography (CT); thyroid cancer; case report

Submitted Mar 04, 2021. Accepted for publication Jun 03, 2021. doi: 10.21037/gs-21-139 View this article at: https://dx.doi.org/10.21037/gs-21-139

Introduction an association between PTACs and other pulmonary abnormalities, including congenital respiratory tract Paratracheal air cysts (PTACs) are collections of air adjacent to abnormalities, obstructive lung diseases, emphysema, upper the trachea. The lesions are often asymptomatic and detected lung fibrosis, chronic cough, and trauma in the thorax. incidentally in routine imaging, such as neck or thoracic computed tomography (CT) scans. The prevalence of these However, few studies have determined these relationships lesions has been reported to be 0.3% to 3.7% (1,2). PTACs (1,2,5-9). Similar to tracheal diverticula, PTAC can cause are usually observed on the right side of the trachea at the level a variety of chronic and recurrent aerodigestive tract of the thoracic inlet. Communication of these lesions with the symptoms (10). Differential diagnosis of PTAC includes trachea is noted in fewer than 10% of cases (1). tracheal diverticulum, Zenker’s diverticulum, pharyngocele, The pathogenesis of PTAC is diverse, and such lesions laryngocele, pneumomediastinum, apical lung hernia, apical are described in both congenital and acquired conditions. A paraseptal lung bulb, and bullae (1,2,11). few studies have considered PTACs and tracheal diverticula Typically, PTACs are asymptomatic, but symptomatic as similar entities (1,3,4). A previous study reported PTACs require treatment. Nonsurgical and conservative

^ ORCID: 0000-0002-7791-2994.

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Figure 1 Incidental paratracheal air cyst in a 68-year-old female with old healed pulmonary tuberculosis. The axial computed tomography (CT) (A) and coronal CT (B) images show a paratracheal air cyst in the right posterolateral aspect of the trachea at the level of the thoracic inlet. Diffuse bronchiectasis was noted on additional thin section CT images. T, trachea; C, paratracheal cyst. management, such as administration of antibiotics, defined, right thyroid nodule measuring approximately mucolytics, and bronchodilators, are used in initial treatment. 2 cm. There was no cervical lymphadenopathy. Laboratory However, in cases in with critical or recurrent symptoms such serum tests including complete blood count, electrolytes, and as compression symptoms (dyspnea, dysphagia, hoarseness), thyroid function were normal. Ultrasound of the neck showed recurrent infections, or chronic cough, surgical intervention a diffusely enlarged thyroid with coarse heterogeneous is recommended (11,12). parenchyma. Multiple, conglomerated, irregular, hypoechoic, In this report, we present a case of asymptomatic nodular lesions were seen in the right mid-lower thyroid. PTAC that was incidentally found in a patient with The lesions measured 2.1 cm in longest diameter on the papillary thyroid carcinoma (PTC). We report the first longitudinal view. Enlarged paratracheal lymph nodes (LNs) case of asymptomatic PTAC that was surgically removed. with a round shape, focal cortical hypertrophy, and 8 mm in Surgical resection enabled us to perform histopathological maximum diameter were identified. examination, which provided insight into the etiology Thoracocervical 64-slice CT scan with intravenous of PTAC, and to review clinical factors that might be contrast showed an approximately 2-cm-sized, ill- associated with its etiology. We present the following case defined, low-density lesion in the right thyroid with in accordance with the CARE reporting checklist (available multiple enlarged LNs in the right paratracheal and at https://dx.doi.org/10.21037/gs-21-139). upper mediastinal region. None of the radiologic findings suggested lateral neck metastasis or pulmonary metastasis. A large ovoid cyst was found incidentally in the right Case presentation posterolateral wall of the trachea at the thoracic inlet Patient level, beneath the collection of enlarged paratracheal LNs. The cyst measured 2.3 cm in longest diameter. Diffuse A 68-year-old woman was referred to our hospital after bronchiectasis was noted in both lungs. Fibrocalcified diagnosis of right thyroid nodule that measured 2 cm and lesions of presumed tuberculous origin (old healed was suspicious for PTC by fine needle aspiration biopsy tuberculosis) were seen in the left upper lobe (Figure 1A,B). (Bethesda category V). She complained of a protruding Pulmonary function test revealed a moderate obstructive neck mass causing neck swelling, neck discomfort, and lung defect with decreased forced expiratory volume in one sore throat. The patient had a history of hypertension second (FEV1) of 73% (1.16/1.58) and a FEV1/expiratory and was taking angiotensin II receptor blockers. She was forced vital capacity (FVC) ratio of 68%. a non-smoker and had no respiratory symptoms. She had also experienced a rear-end collision car accident without Surgery physical injury 20 years prior. Physical examination of the neck revealed a hard, ill- Bilateral total thyroidectomy under general anesthesia

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Figure 2 Histopathological features of paratracheal air cyst. Hematoxylin and eosin (H&E) staining. (A) Cystic lesion with thin-walled epithelium (×1.25); (B) ciliated epithelium with mucin-containing goblet cells (×400); (C) Periodic acid-Schiff (PAS) stain highlights cytoplasmic mucin (×400); (D) magnified submucosal glands below the epithelium (×400).

was indicated for the patient due to the following Pathology conditions: age >55 years, cancer lesion >2 cm in size, Histopathological examination of the right thyroid gland and enlarged central LNs with suspicious features. After revealed an ill-defined infiltrative tumor measuring 2.1 cm right hemithyroidectomy, ipsilateral central compartment × 1.9 cm that was confirmed to be oncocytic variant PTC. neck dissection (CCND) was conducted. The procedure There was no extrathyroidal extension, lymphatic invasion, comprised level VI LNs (prelaryngeal, pretracheal, and paratracheal LNs) and level VII LNs (upper mediastinal or blood vessel invasion by the tumor. Marked chronic LNs). As we proceeded with paratracheal LN dissection, lymphocytic thyroiditis was observed in both glands. No the upper part of an air cyst was found adjacent to the metastasis was found among 15 level VI LNs and 12 level trachea in the right paratracheal region at the thoracic inlet VII LNs (0/27). level. The mass was ovoid and cystic, surrounded by a thin The thin-walled cystic mass resected from the wall, and measured approximately 1.3 cm in diameter. For paratracheal area was inspected. On gross examination, the further LN dissection at level VII, removal of the PTAC resected specimen consisted of a thin-walled cystic mass was inevitable. Because of the considerable volume of the measuring 1.4 cm (Figure 2A). No specific contents or cyst, a 21-gauge syringe needle was used to aspirate it to solid portion was identified. The microscopic findings with reduce its volume; 3 mL of air was aspirated. The mass hematoxylin and eosin (H&E) staining revealed that the was excised, and a subsequent level VII LN dissection and cyst was lined by ciliated columnar epithelium with periodic left hemithyroidectomy were performed sequentially. The acid-Schiff (PAS) stain-positive goblet cells (Figure 2B,C). patient was informed of the concurrent mass removal. The Below the epithelium, a few submucosal serous and mucous patient had an uneventful post-operative recovery. glands were observed (Figure 2D).

Prognosis after surgery The etiology and pathophysiology of PTAC remain unclear. The most popular hypothesis is tracheal mucus There were no postoperative complications. The patient sprouting through weak trachea points due to chronic continued on levothyroxine medication without further inflammation or increased intraluminal pressure (1). The radioactive iodine therapy. After 6 months, follow-up cause of right-sided positioning is probably due to lack of ultrasound showed no evidence of recurrence. Symptoms of support of the left-lying esophagus and the aortic arch (3,9). discomfort in the neck were completely resolved. Thyroid PTACs tend to be located at the point of least resistance, the function test revealed a serum thyroid-stimulating hormone thoracic inlet, which is the transitional point between the (TSH) level of 1.18 µIU/mL, free T4 of 1.6 ng/dL, extrathoracic and intrathoracic trachea. Communication of and T3 of 1.10 ng/mL. Serum thyroglobulin (Tg) level the lesion with the trachea has previously occurred in fewer was undetectable (less than 0.04 ng/mL), and serum Tg than 10% of cases, but several studies have reported higher antibody was 14.8 IU/mL. rates of communication: 34.6%, 37.7%, and 55.0% (2,5,6). Her lung function was monitored on follow-up in the In our patient, the location was consistent with previous Department of Pulmonology every 2 to 3 months. Initially reports at the thoracic inlet, but no visual communication she had neither respiratory symptoms nor breathing was noted between PTAC and the trachea during surgery. difficulty, but after 3 months shortness of breath developed However, histology revealed that the PTAC was lined by after walking up a flight of stairs. The patient was started on ciliated columnar epithelium with PAS stain-positive goblet adrenergic bronchodilator drugs, an inhaler, and mucolytics. cells, and a few submucosal serous and mucous glands were Follow-up chest CT at 6 months was unremarkable with no identified. These microscopic findings, usually seen in cells significant changes. of the respiratory tract, including the trachea and bronchus, The authors are accountable for all aspects of the work in provide strong evidence for the commonly accepted ensuring that questions related to the accuracy or integrity mechanism of “budding of tracheal mucus” (1,5). of any part of the work are appropriately investigated and The association between PTAC and lung abnormalities resolved. All procedures performed in studies involving remains controversial. Respiratory tract abnormalities human participants were in accordance with the ethical (such as bronchomalacia of the right upper lobe bronchus standards of the institutional and/or national research and cystic adenomatoid malformation), obstructive lung committee(s) and with the Helsinki Declaration (as revised diseases (such as chronic obstructive pulmonary disease and in 2013). Written informed consent was obtained from the bronchiectasis), emphysema, inflammatory lung disease patient. (such as upper lung fibrosis), chronic cough, and trauma to the thorax have been investigated. Although several Discussion studies have suggested a positive correlation between PTAC and obstructive lung disease, upper lung fibrosis, and PTACs are usually asymptomatic and found incidentally on lung emphysema (8,9,13,14), others found no significant routine imaging, such as neck or thoracic CT scans. The relationship with lung disease (5-7). prevalence of the lesions has been reported to be 0.3% to Our patient had no respiratory symptoms, but 3.7% (1,2). Some reports, however, described a prevalence emphysematous lung with a fibrocalcified old tuberculous up to 6.5% or 8.1% due to advanced CT technology lesion was noted on CT. Furthermore, pulmonary function resulting in thinner sections and higher spatial resolution tests revealed moderate obstructive lung function. The (5,6). Most studies have shown a higher occurrence of presence of PTAC in the sixth decade of life indicates that PTACs among women (5,6,9,13). The prevalence peak has a congenital cause of PTAC was unlikely. As previously been reported to occur in the fifth to sixth decade of life mentioned, the most reliable pathophysiology of this PTAC (5,7,13,14). In our case, the patient was an asymptomatic was protrusion of tracheal mucosa through weak points 68-year-old female, which agrees well with the common in the trachea, a hypothesis that is supported by the case’s findings in patients with PTAC. histopathologic findings. Weakening of the trachea can The notable characteristic in our case was the size of the result from chronic inflammation or increased intraluminal lesion. Previous reports describe a mean cyst size of 1.4 cm × pressure in the trachea (1). The patient’s lung condition 1.0 cm on CT scan, but the cyst in the present case measured might have contributed to development of PTAC. In 2.3 cm × 1.3 cm, larger than has been described (1,6). addition, she had been involved in a car accident 20 years

© Gland Surgery. All rights reserved. Gland Surg 2021;10(7):2334-2339 | https://dx.doi.org/10.21037/gs-21-139 2338 Kim et al. PTAC with papillary thyroid cancer prior, so traumatic injury cannot be excluded as a cause of disease with impaired lung function or history of trauma increased intraluminal pressure in the trachea. might have contributed to the development of PTAC. Intervention is not usually performed in asymptomatic Future studies with more subjects are needed to determine PTACs; however, patients with symptomatic PTACs if PTAC has any association with obstructive lung disease or (large cyst, cyst rupture, or infected cyst) typically undergo trauma. medical treatment or surgical removal (15-17). In our case, the asymptomatic PTAC was removed for ipsilateral Acknowledgments CCND during thyroid cancer surgery. Surgeons might encounter several cystic masses during thyroid surgery. Funding: None. The differential diagnosis for a right paratracheal cystic lesion at the thoracic inlet level includes parathyroid cyst, Footnote thymic cyst, branchial cleft cyst, bronchogenic cyst, cystic metastatic LN, and neurogenic tumor, among others (18). Reporting Checklist: The authors have completed the PTACs can be differentiated as a “pure air”-containing cyst CARE reporting checklist. Available at https://dx.doi. with no other internal content. org/10.21037/gs-21-139 This report has several limitations. First, determining other clinical characteristics of this disease was not possible Conflicts of Interest: All authors have completed the ICMJE with only one patient. Although several studies have suggested uniform disclosure form (available at https://dx.doi. a positive correlation between PTAC and obstructive lung org/10.21037/gs-21-139). The authors have no conflicts of disease or traumatic injury, it was difficult to determine the interest to declare. relationship between PTAC, an underlying lung condition, and trauma history in this patient. Further evaluations of a Ethical Statement: The authors are accountable for all large group of patients are needed to clarify the associations aspects of the work in ensuring that questions related between PTAC, lung disease, and traumatic injury. Second, to the accuracy or integrity of any part of the work are systemic assessment of etiology was not accomplished. We appropriately investigated and resolved. All procedures performed neck ultrasound and thoracocervical CT scan performed in studies involving human participants were in for preoperative evaluation of thyroid cancer. On CT, no accordance with the ethical standards of the institutional communication was found between PTAC and surrounding and/or national research committee(s) and with the Helsinki organs. However other imaging modalities should be Declaration (as revised in 2013). Written informed consent considered, including esophagography, bronchography, was obtained from the patient. bronchoscopy, expiratory CT, and three-dimensional reconstruction imaging modalities, which could more Open Access Statement: This is an Open Access article accurately assess communication of PTACs with surrounding distributed in accordance with the Creative Commons structures (1,6,19). Attribution-NonCommercial-NoDerivs 4.0 International Based on our experience, we recognize that the clinical License (CC BY-NC-ND 4.0), which permits the non- features of this PTAC were mostly consistent with previous commercial replication and distribution of the article with reports. Specifically, the cyst was incidentally found on a the strict proviso that no changes or edits are made and the CT scan in a woman in her sixties, and it was located in original work is properly cited (including links to both the the right posterior region adjacent to the trachea at the formal publication through the relevant DOI and the license). thoracic inlet level. Unlike previous reports, the cyst was See: https://creativecommons.org/licenses/by-nc-nd/4.0/. large and had to be removed during thyroid cancer surgery. Intervention is not usually necessary, but in this case, References resection was required for appropriate CCND. Resection enabled examination of its pathophysiology, which strongly 1. Goo JM, Im JG, Ahn JM, et al. Right paratracheal air cysts supported a mechanism of tracheal mucus budding through in the thoracic inlet: clinical and radiologic significance. weak points. With only one case, it is impossible to evaluate AJR Am J Roentgenol 1999;173:65-70. correlations between PTAC and other clinical factors. In 2. Buterbaugh JE, Erly WK. Paratracheal air cysts: a common this patient, we could hypothesize that obstructive lung finding on routine CT examinations of the cervical

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Cite this article as: Kim MJ, Jung H, Park CS. Incidental paratracheal air cyst in papillary thyroid cancer patient: a case report. Gland Surg 2021;10(7):2334-2339. doi: 10.21037/gs-21-139